The present invention relates to apparatus for making organic fertilizer, sometimes referred to as compost, or other fermentation products from organic waste materials such as municipal garbage, sewage sludge, animal manure, canning factory wastes and the like.
In my prior patents, U.S. Pat. Nos. 3,138,447 and 3,245,759, a method and apparatus for such manufacture have been described which are designed to produce an efficient and thorough aerobic decomposition of such organic waste materials by maintaining, within the apparatus in which the method is carried out, conditions suitable for optimum propagation of the different types of aerobic bacteria on which such decomposition depends. As described in said patents, the apparatus comprises a digester in the form of a cylindrical drum mounted for rotation on an axis which is slightly inclined towards the discharge end relative to the horizontal. The interior of the digester is divided into a series of compartments or chambers by a plurality of transverse partitions spaced along the axis of rotation. Each partition is provided with transfer buckets which are selectably opened and which, when opened, transfer material from compartment to compartment from the higher to the lower end of the drum, the raw waste organic material being fed into the digester at the higher end and the finished product being withdrawn at the lower end.
The requisite inoculation of the charge in each compartment is effected by retaining a portion of the treated material in each compartment to mix with the material received from the adjacent upstream compartment. In my said prior apparatus, the inoculation material is retained in each compartment by locating the openings in the partitions, which openings communicate with the transfer buckets, displaced a short distance from the periphery of the partition. Such openings are also relatively small compared to the size of the partitions.
As explained in said patents, the method relies upon staging the fermentation process by maintaining optimum but different temperatures in each of the compartments for efficient promotion of the microbial activity. For this purpose air is forced through the entire digester from the discharge or lower end of the drum to the input or higher end, and spent air is selectably and controllably vented from each compartment to maintain the climate therein that is optimum for the microorganisms predominant in the stage associated with such compartment. Efficiency of such method and apparatus depends upon being able to effect rapid transfer of material between compartments causing minimum albeit inevitable interruption of the biological activity. Further important parameters are the speed with which a charge entering a compartment can be mixed with the inoculant retained in such compartment, as well as the capability of retaining at least the necessary minimum and, preferably, an optimum quantity of inoculant.
While the apparatus described in said patents is suitable for carrying out said method, it has been discovered that the efficiency can be increased by increasing the speed with which inter-compartment transfer can be accomplished and, at the same time, modifying the means for automatically retaining the inoculant material in each compartment, whereby more immediate and thus more efficient mixing between the inoculant and incoming charge is effected.